Lab 2: Multiplexed 7-Segment Display

embedded-systems
display-systems
multiplexing
lab-report
Implementation of a multiplexed 7-segment display system, learning about time-division multiplexing and display control techniques
Author

Emmett Stralka

Published

August 29, 2024

Lab 2: Multiplexed 7-Segment Display

Implementation of a multiplexed 7-segment display system, learning about time-division multiplexing and display control techniques

Overview

Lab 2 focuses on implementing a multiplexed 7-segment display system using time-division multiplexing techniques. This lab teaches students about display control algorithms, multiplexing strategies, and the challenges of managing multiple display segments efficiently.

Learning Objectives

  • Understand 7-segment display operation and segment mapping
  • Implement time-division multiplexing for multiple digits
  • Design efficient display update algorithms
  • Optimize timing for flicker-free operation
  • Master hardware interface control for display systems

Step-by-Step Procedure

1. Hardware Setup

  • Connect 7-segment display modules to microcontroller GPIO pins
  • Wire digit selection lines for multiplexing control
  • Verify proper power supply and current limiting resistors
  • Test individual segment functionality

2. Segment Mapping

  • Create lookup table for digit patterns (0-9)
  • Map segment letters (a-g) to corresponding GPIO pins
  • Implement segment pattern encoding for efficient storage
  • Test pattern display for all digits

3. Multiplexing Implementation

  • Design time-division multiplexing algorithm
  • Implement digit selection and segment control
  • Set up timer interrupt for consistent refresh rate
  • Optimize timing to prevent visible flicker

4. Display Control System

  • Create display buffer for storing current values
  • Implement update functions for changing displayed numbers
  • Add support for decimal points and special characters
  • Test with various number combinations

Technical Implementation

The multiplexed display system uses time-division multiplexing to control multiple 7-segment displays with a limited number of GPIO pins. Key technical aspects include:

  • Segment Control: Direct GPIO manipulation for individual segment control
  • Digit Selection: Time-multiplexed digit enable/disable for display selection
  • Refresh Rate: Timer-based updates to maintain flicker-free operation
  • Buffer Management: Efficient storage and update of display values

Performance Optimization

Critical optimization techniques for the multiplexed display: - Optimal Refresh Rate: Balance between flicker prevention and processor overhead - Efficient Pattern Storage: Lookup tables for fast digit pattern retrieval - Minimal GPIO Operations: Reduce unnecessary pin state changes - Interrupt-Driven Updates: Consistent timing without blocking main program flow

Testing and Validation

Functional Tests

  • Individual Digit Test: Verify each digit displays correctly
  • Pattern Test: Confirm all digits 0-9 display proper patterns
  • Multiplexing Test: Ensure smooth switching between digits
  • Flicker Test: Verify no visible flicker at normal viewing distance

Performance Tests

  • Refresh Rate Measurement: Confirm consistent update timing
  • Current Consumption: Monitor power usage during operation
  • Temperature Test: Verify stable operation over extended periods

Troubleshooting Guide

  • Segments not lighting:
    • Check GPIO pin configuration and connections
    • Verify power supply and current limiting resistors
    • Test individual segment functionality
  • Flickering display:
    • Adjust refresh rate timing
    • Check for timing conflicts in main program
    • Verify stable power supply
  • Incorrect digit patterns:
    • Review segment mapping and lookup table
    • Check for bit order issues in pattern encoding
    • Verify GPIO pin assignments

Resources and Documentation

Expected Outcomes

Upon successful completion of Lab 2, students will have implemented a fully functional multiplexed 7-segment display system with flicker-free operation, efficient update algorithms, and proper hardware interface control. This foundation is essential for future display-based projects and user interface development.